The present invention relates to wireless data communication. More particularly, the present invention relates to a novel and improved method and apparatus for code assignment in a spread-spectrum wireless communication system.
In a spread spectrum wireless communication system, a base station communicates with multiple mobile users. In one system, a Code Division Multiple Access (CDMA) system, such as specified in the xe2x80x9cTIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,xe2x80x9d hereinafter referred to as xe2x80x9cthe IS-95 standard,xe2x80x9d or the xe2x80x9cTIA/EIA/IS-2000 Standards for cdma2000 Spread Spectrum Systems,xe2x80x9d hereinafter referred to as xe2x80x9cthe cdma2000 standard,xe2x80x9d codes are applied to the data and control information. The codes identify the target recipient as well as the sender. Operation of a CDMA system is described in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d and also in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d both assigned to the assignee of the present application for patent and hereby expressly incorporated by reference. The forward link from base station to mobile users assigns a unique Walsh code to each mobile with which it transmits, wherein the Walsh code identifies the mobile. Similarly, the reverse link from the mobile user to the base station uses a Pseudorandom Noise (PN) code for channelization.
Alternate spread spectrum systems incorporate a variety of codes for the two-way identification. A problem exists as codes may be reused in neighboring cells and/or sectors, creating interference for adjacent neighbors. Therefore, a method is needed to provide the two-way identification of wireless communications while minimizing and/or reducing the interference experienced by neighboring cells and/or sectors. Similarly, there is a need for a code assignment method that achieves that reduces neighbor interference.
The disclosed embodiments provide a novel and improved method for code assignment in a spread spectrum wireless communication system. In one aspect, in a wireless communication system adapted for Large Area Synchronized-Code Division Multiple Access (LAS-CDMA) transmissions having a plurality of LS codes, a method includes determining a size of an Interference Free Window (IFW), calculating a plurality of subsets from the plurality of LS codes, each subset comprising LS codes as a function of the IFW, assigning a first of the plurality of subsets to a first portion of the system, and assigning a second of the plurality of subsets to a second portion of the system.
In another aspect, a wireless communication system incorporating an LAS-CDMA protocol includes a first cell, the first cell being assigned a first subset of LS codes; and a second cell, the second cell being assigned a second subset of LS codes, wherein the first and second subsets have a null cross-correlation within a predetermined interference free window. Note that the LS codes within the first and second subsets also have a null cross-correlation with a predetermined IFW that is typically wider than that between cells.
In another aspect, in a Large Area Synchronized-Code Division Multiple Access wireless communication system, a method includes transmitting a first communication within a first cell, the first communication identifying at least one mobile station within the first cell by a first LS code within a first subset of LS codes; and transmitting a second communication within a second cell, the second communication identifying at least one mobile station within the second cell by a second LS code within a second subset of LS codes, wherein a cross-correlation of the first and second subsets is null within an interference free window.
In another aspect, a controller in a Large Area Synchronized-Code Division Multiple Access wireless communication system includes a first set of instructions for determining an interference free window size for communications between neighboring cells; and a second set of instructions for determining at least two sets of LS codes based on the interference free window size, a first set for identifying mobile stations in a first cell and a second set for identifying mobile stations in a neighboring cell, wherein the two sets of LS codes have a null cross-correlation within an interference free window. This is also true of the LS codes within each of the subsets with respect to each other.
According to still another aspect, in a Large Area Synchronized-Code Division Multiple Access wireless communication system, the system having a first cell and a first cell neighborhood, a computer data signal is embodied on a carrier wave, the signal including a first portion comprising information for transmission to a first mobile user in a first cell; and a second portion comprising a first LS code corresponding to the first mobile user, wherein the first LS code is part of a first set of LS codes exclusively assigned to the first cell within the first cell neighborhood.